Metal reduction and melting process and apparatus

ABSTRACT

A metal reduction and melting process which involves the heating of a burden comprising a metal containing component and a carbon containing component in a channel type induction furnace in order to reduce such metal containing component, in which at least part of the gaseous products of the process is utilized for preheating the burden; and apparatus for carrying out such preheating.

This application is a national stage of PCT/NL97/00436, filed Jul. 22,1997.

BACKGROUND TO INVENTION

This invention relates to a metal reduction and melting process, such asfor example a steelmaking process, in which a metal and carboncontaining burden is heated in a channel type induction furnace in orderto cause the reduction and melting of the metal containing part of theburden, and apparatus for carrying out such preheating.

PRIOR ART

In a known process in this regard, i.e., that of U.S. Pat. No.5,411,570, where the metal-containing component of the material beingfed to the furnace comprises a metal ore, or a partially reduced metalore (such as sponge iron in the case of an iron-containing burden), andthe carbon-containing component coal; the material is fed substantiallyvertically into the furnace through one or more feed holes located alongthe side of the furnace in a manner so that the burden in the furnaceforms a continuous longitudinally extending heap along each side of thefurnace which floats on the bath of molten metal in the furnace.

In the said arrangement, the resulting gaseous products, mainly CO, andthe volatile matter associated with the coal, are combusted in a cavitylocated in the furnace above the floating burden by burning them withoxygen, which is introduced into such area from outside the furnace.

It is also said that the gases resulting from such combustion, which aretypically at a temperature in the order of 1600° C., can be utilized inthe furnace for heating the burden or, where the material being fed tothe furnace comprises steel scrap or cold iron, the spent carbonmonoxide-related gas may be discharged through the same opening in the

OBJECT OF THE INVENTION

It is an object of the present invention to provide a metal reductionand melting process in which such combustion gases are better utilised.

SUMMARY OF THE INVENTION

According to the invention a metal reduction and melting process whichinvolves the heating of a burden comprising a metal containing componentand a carbon containing component in a channel type induction furnace inorder to reduce such metal containing component, includes the step ofutilising at least part of the gaseous products of such process forpreheating the burden, i.e. prior to its introduction to the furnace.

It will be appreciated that if as a result of such preheating thetemperature of the burden is increased beyond a predetermined value, themetal containing component in the burden will start to be reduced beforethe burden enters the furnace.

This will give rise to at least some gaseous reduction products beingformed in the burden prior to its introduction to the furnace.

The particular temperature at which such reduction starts to take placein the burden before it enters the furnace, will of course be determinedby the nature of the particular metal containing component in theburden.

Furthermore, as a result of such preheating of the burden at least someof the volatile matter associated with the carbon containing compound ofthe burden will also be released in the burden prior to it entering thefurnace.

The aforesaid gaseous products which enter the furnace may accordinglycomprise the aforesaid volatile matter together with the CO and CO₂formed in the said reduction process.

It will be appreciated that such preheating of the burden not only givesrise to a reduced energy requirement in the overall process, but also toan increased throughput for the furnace.

Further according to the invention at least part of the aforesaidgaseous products are burnt with air and/or oxygen in the furnace and thecombustion gases so produced utilised for said preheating of the burden.

Further according to the invention the burden is fed to the furnace inan elongated chamber which is provided with one or more passagesextending around or through the chamber, through which passages the saidcombustion gases can pass in order to preheat the burden in the chamber.

Preferably the chamber and passage(s) are sealed off relative to oneanother so that no gaseous product can pass between them.

In a preferred form of the invention, such a passage may comprise anannular jacket which extends longitudinally around the chamber.

Further according to the invention the one or bottom end of said chambermay extend for such a distance into the furnace that it engages theheaps of burden floating on the bath of molten metal in the furnace.

In this manner the burden in the chamber is prevented from falling freeInto the furnace through such end.

In one form of the invention a positive pressure may be maintained insaid chamber in order to ensure that most of the gaseous products formedin the chamber will pass into the furnace.

Such a pressure may, for example, be brought about by introducing theburden to the chamber by means of a suitable lock system.

In addition, or alternatively, such positive pressure may be maintainedby introducing a pressurised inert gas, such as nitrogen, to the burdenprior to passing it into the chamber.

In one form of the invention at least some of the aforesaid gaseousproducts formed in the burden prior to its introduction to the furnacemay be removed from the burden prior to the burden entering the furnace.

Thus, for example, at least some of the oxidising gases, such as CO₂ andH₂O-vapour, formed in the burden may so be removed from the burden.

The reason for removing such oxidising gases relates to the fact that ifthe temperature in the burden reaches a predetermined value, suchoxidising gases may react with the metal and carbon containingcomponents of the burden thus resulting in the consumption of the carboncontaining compound.

Further according to the invention such oxidising gases may be removedfrom the burden by means of a elongated open ended conduit which extendslongitudinally through said elongated chamber, so that its one or bottomend is located towards the bottom end of the chamber and its other orupper end communicates with a suitable gas withdrawal system, theconduit including over its length at least one gas outlet which islocated at a predetermined level in the chamber.

In use, the conduit will accordingly be surrounded by the burden and itssaid gas outlet located at a predetermined level in the burden.

Further according to the invention said gas outlet of the conduit islocated at a level in the chamber where the burden is at thattemperature just before which said oxidising gases will start to reactwith the metal and carbon containing components of the burden.

Such preferred level may, for example, be determined experimentally by,for example, analysing the gas withdrawn from the conduit.

In addition, or alternatively, the temperature at the gas outlet of theconduit may be measured such as, for example, by means of a thermocoupleor the like.

In practice, once the preferred level of said gas outlet of the conduithas been determined, its position will remain fixed and the temperatureof the burden in said location controlled by, for example, controllingthe rate at which the oxidising gases is removed from the conduit,and/or the rate of the preheating, and/or the rate at which the burdenis fed through the chamber.

In the case where the metal containing compound comprises iron, and thecarbon containing component coal, the aforesaid temperature will be inthe order of 600° C.

The oxidising gases which are so removed may, for example, be utilisedelsewhere or they may be passed to the said passage(s) utilised forpreheating the burden.

Further according to the invention preheated oxygen and/or air are/isintroduced to the conduit towards its said bottom end in order tocombust any CO present in that part of the burden to CO₂, which is thenalso withdrawn through said gas outlet.

In order to ensure that substantially all the CO is converted to CO₂before the gas reaches the said gas outlet, the wall of the chamberimmediately below the gas outlet is maintained at a lower temperaturerelative to the rest of the chamber.

Such lower temperature may be obtained through suitable heat insulation,and/or by delaying the rate at which the burden in the chamber movespast such part of the conduit's wall. This latter operation could, forexample, be effected by increasing the cross sectional width of thechamber in such areas.

Still further according to the invention at least some of the volatilematter associated with the carbon containing components of the burden iscirculated from the said upper end of the conduit towards its saidbottom end, where it can be combusted simultaneously with the CO byoxygen and/or preheated air.

As will be appreciated the heat supplied through such conversion andcombustion will assist in the preheating of the burden.

Said circulation of the volatile matter may be brought about by means ofan elongated open ended pipe of which the one end is located at apredetermined level towards said upper end of the conduit, and the otherend towards said bottom end of the conduit.

Still further according to the invention, the carbon containingcomponent of the burden may be charged to the chamber in such a mannerthat it is distributed towards the outer wall of the chamber, while themetal containing component of the burden is distributed towards theouter wall of said conduit.

In this way the carbon containing component (which provides the carbonwhich is required for the endothermic Boudouard reaction which in turnis required to convert carbon dioxide into carbon monoxide, which isultimately required for reducing the metal in the metal containingcomponent of the burden), is closer to the preheating source than themetal containing component, which in some cases reacts exothermicallywith carbon monoxide.

Further according to the invention the iron containing compound of theburden comprises an iron ore, and the carbon containing component, coal.

The invention will now be described further by way of example withreference to the enclosed drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic cross sectional view of one embodiment of afurnace provided with preheating apparatus according to the invention;and

FIG. 2 is a similar view as that of FIG. 1 with parts shown broken away,of another embodiment of said apparatus.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

In both embodiments of the invention a burden preheating arrangement 10according to the invention is shown as being utilised with a channeltype induction furnace 11.

Furnace 11 comprises an elongated tubular vessel 12 which is of circularconfiguration in cross section and which includes at least two parallelspaced rows of burden feed holes which each extends through the wall ofvessel 12 along opposite sides thereof and of which only one, 13, isshown in detail in the drawings.

Vessel 12 is heated from below by means of two parallel spaced rows ofelectric induction heaters 14.

When used in a steelmaking process, vessel 12 is charged with a quantityof molten steel to form a bath 16, and a burden 15, comprising a mixtureof coal and iron ore, is introduced to vessel 12 through feed holes 13to float on the bath of molten steel 16 in the form of two spaced apartheaps 17 which each extends along a longitudinal side of vessel 12, andabove which a cavity 18 is formed in vessel 12.

Vessel 12 is also provided with a plurality of oxygen burners 19, and atleast one port (not shown) for removing the reduced and molten steelfrom vessel 12.

In the embodiment shown in FIG. 1, arrangement 10 includes an elongatedchamber 20 of which the one end extends through feed hole 13 into theinterior of furnace 11 to such a depth that it engages the upper end ofheap 17.

Burden 15 is fed to chamber 20 via a burden feed bunker 21 and a seriesof lock systems 22.

Chamber 20 is surrounded by an elongated annular passage in the form ofa jacket 23 which has a bottom inlet 24 provided with a nozzle 25 whichpasses through the wall of vessel 12 to communicate with area 18 offurnace 11.

Jacket 23 also includes a top outlet 26 which is connected via a pipe 27to the duct 28 of a gas exhaust system (not shown).

Chamber 20 and jacket 23 are suitably sealed off with respect to eachother to prevent any gas from passing from the one to the other.

In operation, vessel 12 is charged with a supply of molten steel 16, andinduction heaters 14 switched on. A burden 15, comprising a mixture ofcoal and iron ore, is fed from bunker 21 via lock systems 22 and feedholes 13 into vessel 12, to form heaps 17 which float on top of liquidmetal bath 16. The upper end of a heap 17 is engaged by the bottom endof chamber 20 so that the burden at the top of the heap blocks the openend of chamber 20, thus preventing burden 15 from falling freely fromthe open end of chamber 20.

Lock systems 22 ensure that a positive pressure is maintained in chamber20 so that substantially no gas can escape from the cold upper surfaceof burden 15.

The gases, mainly CO, CO₂ and volatile matter resulting from the heatingand consequential reduction of the iron containing component of burden15 are burnt in cavity 18 by the oxygen supplied by burners 19.

The resulting combustion products are fed from area 18 via nozzle 25 andinlet 24 into jacket 23 where they serve to preheat the burden 15located in the bore of chamber 20.

As a result of such preheating of burden 15, the throughput of furnace11 is increased significantly.

The spent combustion gasses passing from jacket 23 via outlet 26 andpipe 27 to duct 28, can be used elsewhere in the process in order toutilise their chemical and/or thermal properties.

At the same time the coal associated volatile matter located in chamber20 can as a result of such preheating of burden 14, be cracked tocarbon, CO and H₂ which can then directly participate in the reductionof burden 15 in pipe 20. As a result of this, the coal and oxygenconsumption per ton of product in the process can also be reducedsignificantly.

In the embodiment shown in FIG. 2, wherein parts corresponding to thoseshown in FIG. 1 are indicated by the same number, a burden 15 is fedfrom feed bunker 21 to the upper end of an elongated chamber 29 of whichthe bottom end communicates with an inlet 13 in vessel 12 of furnace 11.

Chamber 29 is annularly surrounded by an elongated jacket 30 of whichthe bottom end has an outlet 24 which communicates via nozzle 25 witharea 18 of vessel 12.

The upper end of jacket 30.1 has an outlet 26 which communicates via apipe 40 with the duct 28 of a gas withdrawal system (not shown).

The outlet of feed bunker 21 is provided with a gas inlet pipe 30 bymeans of which an inert gas such as nitrogen can be passed into burden15 and so into chamber 29 in order to put the latter under a positivepressure.

Chamber 29 is provided with an elongated open ended conduit 31 of whichthe upper end 32 communicates via a pipe 33 and pipe 27 with duct 28.

The lower end 34 of conduit 31 extends a predetermined depth intochamber 29. More details of this are given later.

When burden 15 is fed through chamber 29 into vessel 12, the burden inchamber 29 will annularly surround conduit 31 and engage its bottom openend 34.

Conduit 31 is provided towards the middle of its length with a series ofapertures 35 which are of such size that gas, but not solid burden 15,can pass through them.

Conduit 31 is also provided with an elongated open ended pipe 36 ofwhich the upper end 37 is located towards the upper end 32 of conduit 31and its lower end 38 towards the lower end 34 of conduit 31.

Conduit 31 is also provided at its open end 34 with the inlet 39 of anoxygen preheated/air burner (not shown).

Conduit 31 is so positioned in chamber 29 that its apertures 35 arelocated in that part of burden 15 where its temperature is in the orderof 600° C. Conduit 31 is furthermore of such a length that its upper end32 is located in that part of burden 15 where its temperature is in theorder of 200° C., and its lower end 34 in that part of burden 15 whereits temperature is in excess of 800° C.

Furnace 12 is operated in the same manner as that described above inrespect of the embodiment of FIG. 1.

During such operation, preheating of the lower end of chamber 29 byjacket 30 to a temperature in the order of 850° C. causes the Boudoardreaction to take place, In this part of burden 15, i.e. C+CO₂→2CO.

Part of such CO will react with the iron component of burden 15 to formCO₂, thus causing the partial reduction of the iron component, i.e.3Fe₂O₃+CO→2Fe₃O₄+CO₂.

The formed CO₂ will flow upwardly in burden 15 until it reachesapertures 35 of conduit 31 through which it is then withdrawn via thebore of conduit 31 and pipes 33 and 27 to duct 28 of the gas exhaustsystem (not shown).

Another part of the CO will flow upwardly in the bore of conduit 31where it will be burnt to CO₂ by oxygen/preheated air burner 39, i.e.2CO+O₂→2C0₂, which CO₂ will then, with the CO₂ passing from apertures35, pass via pipes 33 and 27 to duct 28.

At the same time any volatile matter and water vapour present in theupper parts of burden 15 in chamber 29 will pass from the upper end 37of pipe 36 through its bottom end 38 into the bore of conduit 31 wherethe volatile matter will be combusted by oxygen/preheated air burner 39.

It will be appreciated that the heat developed in the conversion of theCO to CO₂, and the combustion of the volatile matter, will assist inheating up burden 15 in chamber 29.

It will be appreciated further that by locating conduit 31 in the saidposition in chamber 29 where its apertures 35 are located at thatposition where the temperature of the burden 15 is in the order of 600°C., the said CO₂ will be removed from burden 15 before it can react withthe metal and/or carbon containing components of burden 15.

In order to further prevent such reaction from taking place, those partsof the wall of conduit 31 located immediately below apertures 35 may bemaintained at a lower temperature relative to the rest of the wall.This, may, for example be effected through proper heat insulation of thewall and/or by reducing the flow rate of burden 15 through chamber 29 insuch area. The latter operation may, for example, be effected byincreasing the cross sectional width of chamber 29 in such area.

It will be appreciated further that the temperature of the burden at thelower end 34 of conduit 31 can be controlled by controlling any one ormore of the following integers: (1) the rate at which burden 15 is fedthrough chamber 29; (2) the nature of the combustion in conduit 31, and(3) the rate at which the combustion gases are passed through jacket 30.

It will be appreciated still further that, if required, at least part ofthe gases formed in vessel 12 during the reduction of burden 15 can besucked back via inlet 13 into chamber 29 in order for them to beutilised in the reduction and/or preheating of burden 15. The moltenmetal product of furnace 12 can further be treated and collected in theconventional manner.

It will be appreciated that the invention also includes within its scopeapparatus for carrying out the process of the invention substantially asherein described. It will be appreciated further that there are no doubtmany variations in detail possible with a process and apparatusaccording to the invention without departing from the spirit and/orscope of the claims.

Thus, for example, burden 15 may be charged to chamber 29 in such amanner that it is distributed towards the outer wall of the chamber forthe reasons set out above.

What is claimed is:
 1. A metal reduction and melting process whichinvolves the heating of a burden comprising a metal containing compoundand a carbon containing compound in a channel induction furnace in orderto reduce such metal containing compound and to form gaseous products inthe furnace, and to utilize at least part of such gaseous products forpreheating the burden, which process includes the steps of feeding theburden to the furnace in at least one chamber which is provided with atleast one passage extending around or through the at least one chamber,and passing at least some of said gaseous products through the at leastone passage and wherein the at least one chamber and the at least onepassage being sealed off relative to one another so that no gaseousproduct can pass between them.
 2. The process of claim 1 wherein the atleast one passage comprises an annular jacket which extendslongitudinally around the at least one chamber.
 3. The process of claim1 which includes the step of maintaing a positive pressure in the atleast one chamber so that most of the gaseous products formed in the atleast one chamber as a result of the preheating of the burden in the atleast one chamber pass into the furnace.
 4. The process of claim 3wherein the positive pressure is maintained by introducing the burden tothe at least one chamber by means of a lock system.
 5. The process ofclaim 3 wherein the positive pressure is maintained by introducing apressurized inert gas, to the burden prior to passing it into the atleast one chamber.
 6. The process of claim 1 which includes the step ofremoving from the burden prior to the burden entering the furnace atleast some of the gaseous products formed in the burden in the at leastone chamber as a result of the preheating.
 7. The process of claim 6wherein the gaseous products comprise oxidizing gases.
 8. The process ofclaim 7 further including the step of removing the gaseous productsformed in the burden by means of an elongated open ended conduit whichextends longitudinally through the chamber, so that a bottom end of theconduit is located towards the bottom end of the chamber and an upperend of the conduit communicates with a gas exhaust system, the conduitincluding over its length at least one gas aperture which is located ata level in the chamber where the burden is at a temperature just beforewhich the oxidizing gases in the burden will start to react with themetal and carbon containing compounds of the burden to form productsincluding at least CO, CO₂ and other volatile matter associated with thecarbon containing component of the burden.
 9. The process of claim 8wherein the level of the gas aperture of the conduit is determined byanalyzing the gas withdrawn from the conduit for its CO and CO₂ content.10. The process of claim 8 which includes the step of measuring thetemperature at the gas aperture of the conduit by means of a heatmeasuring device.
 11. The process of claim 10 wherein the heat measuringdevice is a thermocouple.
 12. The process of claim 8 wherein once thelevel of the gas aperture of the conduit has been determined, itsposition remains fixed, and the temperature of the burden in saidlocation is controlled by controlling at least one of the following: therate at which the oxidizing gases is removed from the conduit; the rateof the preheating and; the rate at which the burden is fed through thechamber.
 13. The process of claim 8, which further includes the step ofcirculating at least some of the volatile matter from the burden at thebottom end of the conduit towards the upper end of the conduit, andcombusting it simultaneously with the CO present, by means of oxygenand/or preheated air provided to that part of the chamber.
 14. Theprocess of claim 13 which includes the step of bringing about saidcirculation of the volatile matter by means of an elongated open endedpipe located inside the container, the one end of the pipe being locatedtowards said upper end of the conduit in a manner so that itcommunicates with the burden, and the other end of the pipe beinglocated towards said bottom end of the conduit.
 15. The process of claim7 wherein the oxidizing gases include CO₂ and H₂O vapor.
 16. The processof claim 6 which includes the step of utilizing the gaseous products soremoved elsewhere in the process or passing them to the at least onepassage utilized from preheating the burden.
 17. The process of claim 6wherein the gaseous products comprise CO, and further including the stepof introducing preheated oxygen and/or air to the conduit towards itssaid bottom end in order to combust to CO₂ any CO present in that partof the burden.
 18. The process of claim 17 which includes the step ofmaintaining a part of the wall of the chamber immediately below the gasaperture at a lower temperature relative to the rest of the chamber sothat substantially all the CO is converted to CO₂ before the gas reachessaid gas aperture.
 19. The process of claim 18 wherein the lowertemperature is effected by at least one of the following steps: (a) heatinsulation of the said part of the wall of the chamber, and (b) delayingthe rate at which the burden in the chamber moves past such part of thechamber's wall.
 20. The process of claim 18 wherein the lowertemperature is effected by employing a chamber of which the crosssectional width is larger in said part.
 21. The process of claim 1wherein the carbon containing component of the burden is charged to theat least one chamber in such a manner that it is distributed towards theouter wall of the at least one chamber.
 22. The process of claim 1wherein the iron containing compound of the burden comprises iron ore,and the carbon containing component, coal.
 23. The process of claim 1,wherein air and/or oxygen is supplied to the furnace, and wherein atleast part of the gaseous products comprises gases produced by burningin the furnace the gases resulting from the process with the air and/oroxygen supplied to the furnace.
 24. The process of claim 1 which iscarried out in such a manner that at least one heap of burden materialis formed which floats on a bath of molten metal in the furnace, andwherein the one or bottom end of the at least one chamber extends forsuch a distance into the furnace that it engages the heap of burden inthe furnace.
 25. An apparatus for preheating the burden of a metalreduction and melting process which involves the heating of a burdencomprising a metal containing component and a carbon containingcomponent in a channel induction furnace in order to reduce such metalcontaining component and to form gaseous products in the furnace; andwhich involves utilizing at least part of the such gaseous products forpreheating the burden, wherein the apparatus comprises at least onechamber through which the burden is fed to the furnace, and one or morepassages extending around or through the at least one chamber, throughwhich passages gaseous products formed in the process pass in order topreheat the burden in the at least one chamber; and the at least onechamber and the at least one passage being sealed off relative to oneanother so that no gaseous product can pass between them.
 26. Theapparatus of claim 25 wherein the at least one passage comprises anannular jacket which extends longitudinally around the chamber.
 27. Theapparatus of claim 25 wherein the one end of the at least one chamberextends for such a distance into the furnace engaging a heap of burdenfloating on a bath of molten metal in the furnace.
 28. The apparatus ofclaim 25 wherein the at least one chamber includes a lock system forfeeding the burden to the chamber so that a positive pressure ismaintained in the chamber and so that most of the gaseous productsformed in the chamber as a result of the preheating of the burden in thechamber pass into the furnace.
 29. The apparatus of claim 25 wherein theat least one chamber includes means for introducing a pressurized gas tothe burden prior to passing it into the at least one chamber in order tomaintain a positive pressure in the at least one chamber.
 30. Theapparatus of claim 25, wherein the at least one chamber includes anelongated open ended conduit which extends longitudinally through the atleast one chamber, so that a bottom end is located towards the bottomend of the chamber and an upper end communicates with a gas withdrawalsystem provided with the apparatus, the conduit including over itslength at least one aperture which is located at a level in the chamberwhere the burden is at a temperature just before which oxidizing gasesin the burden will start to react with the metal and carbon containingcomponents of the burden to form products comprising at least one of CO,CO₂, and volatile matter associated with the carbon containing compoundof the burden, through the at least one aperture at least some of thegaseous products formed in the burden prior to its introduction to thefurnace is removed from the burden prior the burden entering thefurnace.
 31. The apparatus of claim 30, wherein the products formed inthe burden comprise CO, and the at least one chamber includes means forintroducing preheated oxygen and/or air to the conduit towards its saidbottom end to combust to CO₂ any CO present in that part of the burden.32. The apparatus of claim 31 wherein a part of the wall of the at leastone chamber immediately below the gas aperture is maintained at a lowertemperature relative to the rest of the chamber so that substantiallyall the CO is converted to CO₂ before the gas reaches the gas aperture.33. The apparatus of claim 32 wherein the lower temperature is effectedthrough at least one of the following manners: (a) heat insulationapplied to the part of the chamber's wall, and (b) increasing thecross-sectional width of the chamber in the part of the wall.
 34. Theapparatus of claim 30 including an elongated open ended pipe locatedinside the conduit, one end of the pipe being located towards said upperend of the conduit, and its other end being located towards said bottomend of the conduit, the pipe being intended for circulating at leastsome of the volatile matter associated with the carbon containingcomponent of the burden from said upper end of the conduit towards saidbottom end of the conduit, where it can be combusted simultaneously withany CO present by means of preheated oxygen and/or air.